The present invention relates to a device for exchanging heat between air flowing toward or around said device and a fluid flowing partially through said device, in particular to a charge-air cooler for internal combustion engines as they are used in particular in the field of motor vehicles.
Such heat exchangers are generally, and charge-air coolers specially known from the prior art.
Such a known charge-air cooler for a motor vehicle serves to cool down the temperature of charged air supplied from a turbocharger or a compressor to an internal combustion engine of a motor vehicle which can increase the power of the internal combustion engine.
FIG. 4 shows such a charge-air cooler 400, in this case a multiple-row type, for a motor vehicle as known in the prior art.
As FIG. 4 shows, the charge-air cooler 400 comprises a plurality of flat pipes 401 formed by extrusion molding of an aluminum alloy.
The pipes 401 are arranged in several parallel planes where said pipes 401 are also arranged parallel relative each other in each plane.
Each pipe 401 comprises a plurality of refrigerant paths (refrigerant ducts) running substantially parallel relative a longitudinal direction of the pipe 401 and being circular in cross-section and with refrigerant flowing through.
As FIG. 4 further shows, a plurality of corrugated aluminum fins (cooling fins) 402 which are formed by means of a roller and arranged between adjacent pipes 401.
FIG. 5 shows such a fin 402 in detail.
In cross-section, the prior art fin is wave-like or U-/W-like in shape. At the highest places 501, 502 and the lowest places 503 of the cross-section or the contact faces 504, 505, 506 formed by said highest and lowest places 501 to 503 and running in longitudinal direction of the fin 402, each fin 402 is solder-joined with a respective pipe 401.
Said pipes 401 and fins 402 form a core section 403 of the prior art charge-air cooler.
End plates 404 for reinforcing the core section 403 are arranged both at the top and the bottom end of the core section 403 according to FIG. 4 and soldered to the pipes 401 and the fins 402 by means of solder plated or coated, respectively, to both side faces of the fins 402.
A pair of header tanks 405 is joined to each flow duct end of the pipes 401 to be flow-tight and to extend in a direction perpendicular to the longitudinal axis of each pipe 401.
A flow-tight joining is to be understood such as to allow liquid and/or gaseous fluids such as the refrigerant, to flow through said joint which is fluid-tight and/or gastight.
The high temperature charge air at approximately 270° C. flows toward or around the core section 403 of the charge-air cooler wherein heat is exchanged between the charge air and the refrigerant so as to cool down the charge air.
In heat exchange, heat is removed, from the hot charge air via the fins 402 and via the pipes 401 joined to the fins 402 via the contact surfaces 504, 505, 506, to enter the refrigerant which thus heats up considerably.
It may occur precisely in first or front—relative the approach or approaching direction of the charge air at the core section 403—refrigerant ducts (critical profiles or block regions) where the approaching charge air is still highest in temperature, that this type of heat exchange may led to that the coolant flowing there, i.e. in said first coolant ducts, heats up beyond its boiling point.
Such exceeding the boiling point of the coolant results in bubbles appearing in the coolant and thus in problems of erosion and cavities.
This kind of problem with this charge-air cooler can also occur with charge-air coolers generally in the case of high-temperature approaching air.
It is therefore the object of the present invention to provide a heat exchanger which is improved, with respect to exceeding the boiling point and the ensuing problems, compared to the prior art described above.